Science of Water : Concepts and Applications

146 The Science of Water: Concepts and Applications
Whenever possible, persons in the out-of-doors should carry drinking water of known purity
with them. When this is not practical, and when water from streams, lakes, ponds, and other outdoor
sources must be used, time should be taken to properly disinfect the water before drinking it.
Cryptosporidium
Ernest E. Tyzzer fi rst described the protozoan parasite Cryptosporidium in 1907. Tyzzer frequently
found a parasite in the gastric glands of laboratory mice. Tyzzer identifi ed the parasite as a sporozoan,
but of uncertain taxonomic status; he named it Cryptosporidium muris. Later, in 1910, after
a more detailed study, he proposed Cryptosporidium as a new genus and C. muris as the type of
species. Amazingly, except for developmental stages, Tyzzer’s original description of the life cycle
(see Figure 5.10) was later confi rmed by electron microscopy. Later, in 1912, Tyzzer described a new
species, Cryptosporidium parvum (Tyzzer, 1912).
For almost 50 years, Tyzzer’s discovery of the genus Cryptosporidium (because it appeared to
be of no medical or economic importance) remained (like himself) relatively obscure. However,
slight rumblings of the genus’ importance were felt in the medical community when Slavin wrote
about a new species, Cryptosporidium meleagridis, associated with illness and death in turkeys
(Tyzzer, 1912). Interest remained slight even when Cryptosporidium was found to be associated
with bovine diarrhea (Panciera et al., 1971).
Not until 1982 did worldwide interest focus in on the study of organisms in the genus
Cryptosporidium. During this period, the medical community and other interested parties were
beginning to attempt a full-scale, frantic effort to fi nd out as much as possible about acquired
immune defi ciency syndrome (AIDS). The CDC reported that 21 AIDS-infected males from six
large cities in the United States had severe protracted diarrhea caused by Cryptosporidium.
Sporozoite Trophozoite Type I Meront
Auto
infection
Thin Walled
Oocysts
Excystation
Host Epithelial
Cell
Ingestion
Thick Walled
Oocysts
Exit From
Body
Mature Oocyst Immature Oocyst
FIGURE 5.10 Life cycle of Cryptosporidium parvum.
Microgamont
Macrogamont
Merozoite
Merozoite Type II Meront